The Energy storage technology is the key to solve the randomness and volatility of wind and photovoltaic power generation in microgrids, but single energy storage has great limitations in performance. In addition, the energy storage system may be in overcharged and deep-discharged states if the power fluctuates greatly, which reduces the performance of the energy storage system and cannot guarantee the stability of the system. In this regard, this paper improves the charge-discharge protection strategy with quadratic adjustment function based on the state-of-charge (SOC) of the energy storage system and applies it to the HESS (hybrid energy storage system) consisting of SMES (superconducting magnetic energy storage) and BES (battery energy storage). At the same time, the DC/AC converter adopts the V/f control method to realize the stable operation of the island system. The simulation results show that the SMES can quickly compensate for the power shortage before the full response of the BES, which indicates that the HESS has compensatory and suppressive effects on power fluctuations obviously. The voltage fluctuation of DC bus is suppressed and prolonged when the energy storage system enters the overcharge or deep-discharge state.
 

charge-discharge protection strategy, hybrid energy storage system (HESS), superconducting magnetic energy storage (SMES), state-of-charge (SOC), V/f control